U.S. Pat. No.4,303,904, to Chasek, for example, discloses a system for a road toll facility where radio communication with a vehicle is used to perform an identification and payment operation. The operation should be completed even if the vehicle passes at high speed. To obtain a sufficiently selective communication even if several vehicles pass the road toll facility simultaneously, shortwave radiowaves, such as microwaves, with extremely limited range are used. This means that the operation must be performed while the vehicle passes a relatively short distance which gives a very short available time for the operation if the vehicle travels at high speed.
If the operation comprises several steps, which often must be the case, it is a problem to perform the whole operation in the short time available. To solve this problem, it has been suggested in, for example, U.S. Pat. No. 5,144,553, to Hassel, to divide the communication cycle among several units in the road toll facility. According to Hassel, a first part of the operation can be performed in a first unit in the traveling direction of the vehicle. The operation must be continued by a second unit and concluded by a third unit.
Such an arrangement will naturally be more expensive than an arrangement in which only one communication unit is required. This additionally results in an extended facility along the passage, which is not desirable. For each communication unit, the equipment usually requires a gantry mounted above the road. Several such gantries, one after the other, will be less aesthetically appealing and result in higher installation and maintenance costs.